Retinoic acid is an essential substance for the growth or life support of mammals including humans. It is known to have various effects, for example, upon ontogenesis, it serves as a morphogenetic factor, while in the adult body, it has effects on the differentiation and proliferation of cells. Described specifically, it is known to take part in the keratinization reaction, hair formation, sebaceous gland function or the like in the epidermis; the metabolism of bone or cartilage in the connective tissue; immunnomodulatory in the immune system; differentiation of neurocytes in the nerve system; differentiation and proliferation of hemocytes in the blood system; and lipid metabolism, mineral metabolism and basal metabolism. A wide variety of physiological effects of retinoic acid as exemplified above are exhibited by its various control mechanisms such as expression regulation of a transcription activator through an intranuclear retinoid receptor (RARs, RXRs) family, regulation of the hormone secretion or function at the target organ, regulation of growth factors such as EGF receptor or TGF.alpha., expression regulation of enzymes such as collagenase, tissue plasminogen activator or tyrosine kinase, and production regulation of cytokine such as IL-6.
In recent years, the relationship between these physiological effects of retinoic acid and various morbid conditions has come to be apparent. Particularly in some cancers typified by acute myelocytic leukemia, differentiation and induction treatment by using all-trans retinoic acid has drawn attentions as a novel therapeutic method of these cancers.
Retinoic acid, however, is found to involve various problems such as appearance of resistance caused by induction of P450 and expression of side effects due to its accumulation. Under such situations, there is accordingly a strong demand for the development of a novel retinoid-related compound, instead of retinoic acid, as a preventive and/or therapeutic for various diseases.